What is Article 4.2? Who is in the Umbrella group?

Global warming potential. A relative measure of how much heat a greenhouse gas traps in the atmosphere. Specifically, GWP is an index that displays the combined effect of the differing times greenhouse gases remain in the atmosphere and their relative effectiveness in absorbing outgoing infrared radiation - causing a rise in global temperatures. It compares the amount of heat trapped by a certain mass of a gas to the amount of heat trapped by a similar mass of carbon dioxide. GWP is thus expressed as a factor of carbon dioxide (reference gas), and is calculated over a specific time horizon, usually 20, 100 or 500 years.